[opendtv] Re: Panasonic's AG-HVX200
- From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 28 Apr 2005 17:04:56 +0100
No, it's a multiplier all right. Generally it deals with small-signal
excursions. This means that the mtf can exceed unity, where contrast is
actually enhanced. This odd situation happens in negative film, where grains
migrate towards each other under ionic attractive forces while the layers
are wet during processing. The 1-dimensional MTF plot of mtf versus
frequency is actually a frequency response, the mtf value at any frequency
is the gain (or attenuation) at that frequency.
If you know the MTF you can correct for it by building a multiplying
correction in the same number of dimensions. At it's crudest, this is the
"aperture correction" found in cameras (not "detail correction", that's a
subjective mangling of the frequency response).
----- Original Message -----
From: "Tom Barry" <trbarry@xxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Thursday, April 28, 2005 2:49 PM
Subject: [opendtv] Re: Panasonic's AG-HVX200
> Alan Roberts wrote:
>
> > The mtf (lower case) is the "modulation transfer factor". It is, at any
spot
> > frequency (or aperture, or focal length, of position with the frame) the
> > gain of the device. So, if you put a sinusoidal signal into the device
> > (lens, display, camera, whatever) at a particular frequency, the mtf is
the
> > multiplier that it applies to that frequency.
> >
>
> Alan -
>
> Thanks, I've seen the Canon article.
>
> But mtf must be more than just a multiplier factor. If I take a
> sinusoidal signal and multiply it by .5 then the amplitude is only
> half as much but no information has yet been lost, barring
> quantization. I could multiply it by 2 later and get it back. It
> is only when errors (random info) are introduced that information
> goes away. But I'm not sure how this figures in gain or mtf and
> I'm not sure how that part is supposed to be measured.
>
> I realize there are many sources of errors, A/D noise,
> quantization noise, various optical, electronic, and digital
> filters etc. and each contributes in complex ways to lowered mtf
> (either case). But I still can't quite visualize what is being
> measured when "contrast" is lowered.
>
> What am I missing here?
>
> - Tom
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